Process for obtaining a tanning agent from waste sulphite liquor



May 6, 1941. HCNIG 2,241,305

PROCESS FOR OBTAINING A TANNING AGENT FROM WASTE SULPHITE LIQUOR Filed Feb. 23. 19:9

c Cezcseal Hem/m5 Hog/j Patented May 6, 1941 PROCESS FOR OBTAINING A TANNING AGENT FROM WASTE SULPHITE LIQUOR Max Hiinig, deceased, by Heinrich Hiinig, legal representative, Brunn, Czechoslovakia, assignor of thirty per cent to iWilhelm Feith, Brunn,

Czechoslovakia Application February 23, 1939, Serial No. 258,106 In Czechoslovakia July 9, 1936 2 Claims.

The object of this invention is to improve the process of obtaining true tanning substances from sulphite cellulose waste liquors and obtain a tanning substance freer from harmful impurities. This is accomplished by the steps herein set forth.

It is already known from scientific publications that 'it is possible to convert thelignosulphonic acids of sulphite cellulose waste liquors into true tanning substances by subjecting the lignosulphonic acids to an alkaline hydrolysis. Partial splitting of these compounds takes place with elimination of the sulphonic acid group (SOzH) and substitution thereof by an hydroxyl group (OH). These known facts however have not made any technical utilisation possible, more particularly because up to now it has been possible to convert in this way only a small fraction of the lignosulphonic acids (up to about 20%) into true tanning substances. According to the invention this drawback is removed by the fact, which renders possible large-scale technical utilisation, that products are obtained containing at least two parts of tanning substances to one part of non-tanning substance, the process being carried out with gradual pressure rise up to 15 atm. with continuous stirring and heating up to the boiling temperature and the said final pressure being maintained at the boiling temperature for one and one-half hours. scribed below in detail, as well as the possible obtention of auxiliary products.

The process according to the invention can for example be carried out somewhat as follows with the aid of the sedimenting container and the, autoclave shown in the accompanying drawing.

The clear acid waste liquor, freed in suitable manner from the coarse mechanical impurities, is, for the purpose of imparting to it the necessary pH value of 9, first of all treated in a cast iron autoclave provided with stirring mechanism with 10 kg. of freshly burnt lime which has been slaked to a thin pulpy milk of lime for each cubic meter of waste liquor, and the whole is gradually heated, say within an hour and a half, up to a pressure of atm. with continuous powerful actuation of the stirring mechanism up to boiling temperature, and maintained at this pressure and boiling temperature for one and a half hours. substantially exceeded and in any case is kept below atm. and that the heating at this pressure likewise does not last substantially longer than an hour and a half and in no case exceeds two hours. Settling of the precipitate which The new process is de- It is important that this pressure be not rise slowly at I in a conically shaped sediment-- ing container I of suitable capacity in order to give the readily depositable precipitate time and opportunity to sediment as completely as possible. The conical part of the sedimenting cylinder is closed off at the top by means of a sand filter 2 in order to allow the ascending clarifying liquid to leave at 3 perfectly clear, whilst at the bottom the sedimenting vessel at 4 transfers the thick pulpy moist sludge which has settled to a centrifuge drum with automatic discharge device for the purpose of dehydrating the sludge as far as practicable by centrifuging. The clear dark brown liquor completely freed from sludge contains the water-soluble lime salts of the true tanning substance which is formed, van'illin also being formed, this appearing as a regular byproduct accompanying. the true tanning substance formed.

According to the degree of dehydration produced, on an average from each cubic meter of liquor about 155 kg. of moist sludge could be obtained with an average dry substance content of 52.7 kg.

These 52.? kg. of dry mud consist on an average of:

(i) 13.2 kg. CaSOa, equivalent to 7.04 kg. S02

or to 3.51 kg. of sulphur;

(ii) 29.8 kg. of lignosulphonic acid insoluble in hydrochloric acid;

(iii) 9.7 kg. of calcium carbonate.

The 3.51 kg. of sulphur of the dry sludge correspond to about of the organically bound sulphur of the lignosulphonic acid, that is to say about 60% of the lignosulphonic acid is converted according to the new process into true tanning substance.

It was thus found that the lignin complex is bound to the sulphur compounds with different strengths; for about 20% of the lignosulphonic acid present the splitting takes place at atmospheric pressure, for a further approximately 40% under a pressure of about 15 atmospheres, whilst the remaining fraction is not capable of being split up.

According to the elementary analysis carried out the lignosulphonic acid insoluble in hydrochloric acid has a heating value of over 6000 calories, and consequently this waste product present in quantities of about 30 kg. per cubic metre can be used for heating purposes. Since further this waste product has a sulphur content exceeding 3.5%, it is also possible, as experiments have shown, to prepare brown and brown-black sulphurdyes or pigments from the same.

The liquor freed from sludge contains, besides the obtained true tanning substance and the vanillin formed, the lime salts of acetic and formic acids already present in the liquor, which also can be recovered. On an average; about 36 kg. of 80% calcium acetate can be caused to separate out per cubic metre of waste liquor. Finally, the recovery of the sulphurous acid is also possible, by decomposing the calcium sulphite (CaSOz) contained in the insoluble sludge separated off by means of a dilute mineral acid,

advantageously by means of hydrochloric acid.

The true tanning substance obtained from the liquor, which shows a very characteristic composition as regards the proportion between nontanning substance and tanning substance and in fact to one part of non-tanning substance there may be more than two parts of tanning substance, when it is completely freed ,irom the insoluble constituents can not only be used for tanning purposes but also as binding agent for ores and fuel waste, and is particularly suited for this purpose in view of the fact that it can be made approximately sulphur-free, which is of especial importance for the briquetting of ores and fuels.

The product obtained is also distinguished by its great emulsion capability for fats, oils and similar substances, and therefore can find diverse use as emulsifier, especially after extensive desulphurisation.

What is claimed is:

1. A process for obtaining genuine tanning substances from sulphite waste liquors consisting in adjusting the waste liquor, freed from mechanical impurities, to a pH value of 9 by means of lime, heating the liquor in a confined space whilst continuously stirring until a pressure of about 15 atm. is set up, maintaining 'the mixture at the boiling temperature under this pressure for about one and one-half hours whilst continuously stirring, neutralising the free caustic lime' still present in the hot state, and removing the sediment from the tanning liquor.

2. A process as claimed in claim 1 in which the neutralisation of the free caustic lime is effected by means of carbon dioxide.

HEINRICH HGNIG, Legal Representative of M an: Hom'g, Deceased. 

